Stability at the Brain and Synapse Levels

Different people have different temperaments, moods, and behavior profiles that tend to remain constant over a lifetime. Are these temperamental distinctions also reflected in basic brain differences? Schwartz et al. studied the well-established temperamental differences of inhibited versus uninhibited behavior to novelty. They found that people classified in terms of these temperamental categories at the age of 2 showed differential fMRI responses to unfamiliar faces in the brain structure of the amygdala when tested as adults. How stable is a synapse that has just undergone long-term potentiation (LTP) or long-term depression (LTD) in real life? Zhuo et al. (see the Perspective by Chiu and Weliky) induced synaptic plasticity in the retinotectal system of the frog Xenopus. However, in a time window of about 20 minutes, subsequent spontaneous or uncorrelated activity could diminish or even reverse previously induced LTP or LTD. Stable and long-lasting changes in synaptic strength could only be induced if the induction protocol was repeated several times in a spaced fashion, with intervals of several minutes between the plasticity induction events.